Schizophrenia is a debilitating disorder affecting the psychic and motor functions of the brain. It is typically diagnosed in individuals in their early to mid-twenties and symptoms include hallucinations and delusions or at the other extreme, anhedonia or social withdrawal. Across the spectrum, the symptoms are indicative of cognitive impairment and functional disabilities. Notwithstanding improvements in antipsychotic treatments, current therapies, including typical (haloperidol) and atypical (clozapine or olanzapine) antipsychotics, have been less than acceptable and result in an extremely high rate of noncompliance or discontinuation of medication.
Dissatisfaction with therapy is attributed to lack of efficacy or intolerable and unacceptable side effects. The side effects have been associated with significant metabolic, extrapyramidal, prolactic and cardiac adverse events. See, Lieberman et al., N. Engl. J. Med. (2005) 353:1209-1223.
While multiple pathways are believed to be involved with the pathogenesis of schizophrenia leading to psychosis and cognition deficits, much attention has focused on the role of glutamate/NMDA dysfunction associated with cyclic guanosine monophosphate (cGMP) levels and the dopaminergic D2 receptor associated with cyclic adenosine monophosphate (cAMP). These ubiquitous second messengers are responsible for altering the function of many intracellular proteins. Cyclic AMP is thought to regulate the activity of cAMP-dependent protein kinase (PKA), which in turn phosphorylates and regulates many types of proteins including ion channels, enzymes and transcription factors. Similarly, cGMP is also responsible for downstream regulation of kinases and ion channels.
One pathway for affecting the levels of cyclic nucleotides, such as cAMP and cGMP, is to alter or regulate the enzymes that degrade these enzymes, known as 3′,5′-cyclic nucleotide specific phosphodiesterases (PDEs). The PDE superfamily includes twenty-one genes that encode for eleven families of PDEs. These families are further subdivided based on catalytic domain homology and substrate specificity and include the 1) cAMP specific, PDE4A-D, 7A and 7B, and 8A and 8B, 2) cGMP specific, PDE 5A, 6A-C, and 9A, and 3) those that are dual substrate, PDE 1A-C, 2A, 3A and 3B, 10A, and 11A. The homology between the families, ranging from 20% to 45%, suggests that it may be possible to develop selective inhibitors for each of these families.
PDE2 is highly expressed in the brain, but is also found in many other tissues as well, and therefore has a broad array of function and utility (J. A. Beavo, et al., Rev. Physio. Biochem. Pharm., 135, 67 (1999)). Amongst others, PDE2 has been shown to have therapeutic potential in neuronal development, learning, and memory (W. C. G. van Staveren, et. al., Brain Res., 888, 275 (2001) and J. O'Donnell, et. al., J. Pharm. Exp. Ther., 302, 249 (2002)); prolactin and aldosterone secretion (M. O. Velardez, et. al., Eur. J. Endo., 143, 279 (2000) and N. Gallo-Payet, et. al., Endo., 140, 3594 (1999)); bone cell differentiation, growth, and bone resorption (C. Allardt-Lamberg, et. al., Biochem. Pharm., 59, 1133 (2000) and S. Wakabayashi, et. al., J. Bone, Miner. Res., 17, 249 (2002); immunological response (M. D. Houslay, et. al., Cell. Signal., 8, 97 (1996); vascular angiogenesis (T. Keravis, et. al., J. Vasc. Res., 37, 235 (2000); inflammatory cell transit (S. L. Wolda, et. al., J. Histochem. Cytochem., 47, 895 (1999); cardiac contraction (R. Fischmeister, et. al., J. Clin. Invest., 99, 2710 (1997), P. Donzeau-Gouge, et al., J. Physiol., 533, 329 (2001), and D. J. Paterson, et. Al., Card. Res., 52, 446 (2001); platelet aggregation (R. J. Haslam, et. Al., Biochem. J., 323, 371 (1997); female sexual arousal disorder (C. P. Wayman, et. al., EP Patent Publications EP10977707 and EP1097706; osteoarthritis pain (M. Plummer et, al., Bioorganic & Medicinal Chemistry Letters, 23(11), 3438-3442 and 3443-3447 (2013)); malignant melanoma (H. Morita, et al., Oncology Reports, 29, 1275-1284, 2013; and hypoxic pulmonary vasoconstriction (J. Haynes, et. al., J. Pharm. Exp. Ther., 276, 752 (1996). See also 2-Substituted-4,5-dihydroxypyrimidine-6-carboxamide Antiviral Targeted Libraries, Vincent Boyd et al., Journal of Combinatorial Chemistry (2009), 11(6), 1100-1104; From Dihydroxypyrimidine Carboxylic Acids to Carboxamide HIV-1 Integrase Inhibitors: SAR Around the Amide Moiety, Alessia Petrocchi et al., Bioorganic & Medicinal Chemistry Letters (2007), 17(2), 350-353; Dihydroxypyrimidine-4-carboxamides as Novel Potent and Selective HIV Integrase Inhibitors, Paola Pare et al., Journal of Medicinal Chemistry (2007), 50(9), 2225-2239; US2007135457, WO2012151567, US20090253677, US20070281917, WO2004096128, WO2003035077, WO2003035076, WO2007058646, WO2009117540, and U.S. Pat. No. 7,419,969.
Inhibition of PDE2 (e.g., PDE2A) has been shown to enhance cognitive function across multiple preclinical models of cognitive performance that reflect improvements in recognition memory, social interactions and working memory, which are all deficient in schizophrenia (Boess et al., Inhibition of Phosphodiesterase 2 Increases Neuronal cGMP, Synaptic Plasticity and Memory Performance, Neuropharmacology, 47(7):1081-92, 2004). PDE2A inhibition was also shown to improve cognitive deficits that develop in aging and Alzheimer's disease (Domek-Lopacinska and Strosznajder, The Effect of Selective Inhibition of Cyclic GMP Hydrolvzing Phosphodiesterases 2 and 5 on Learning and Memory Processes and Nitric Oxide Synthetase Activity in Brain During Aging, Brain Research, 1216:68-77, 2008). The role of PDE2 inhibition in cognitive disorders was also shown in Brandon et al., Potential CNS Applications for Phosphodiesterase Enzyme Inhibitors, Annual Reports in Medicinal Chemistry 42: 4-5, 2007 (compound BAY 60-7550 was reported to have significant potency at other PDE isoforms, had high clearance and limited brain penetration). See also Jorgenson, et al, Annual Reports in Medicinal Chemistry 48: 37-55, 2013. “Selective Inhibitors of PDE2, PDE9, and PDE10: Modulators of Activity of the Central Nervous System”.
PDE2 inhibitors have also been shown to have efficacy in preclinical models of anxiety and depression (Masood et al., Anxiolytic Effects of Phosphodiesterase-2 Inhibitors Associated with Increased cGMP Signaling, JPET 331(2):690-699, 2009; Masood et al., Reversal of Oxidative Stress-Induced Anxiety by Inhibition of Phosphodiesterase-2 in Mice, JPET 326(2):369-379, 2008; Reierson et al., Repeated Antidepressant Therapy Increases Cyclic GMP Signaling in Rat Hippocampus, Neurosci. Lett., 466(3):149-53, 2009). See also Ducrot et al., CoMFA and CoMSIA 3D-quantitative structure-activity relationship model on benzodiazepine derivatives, inhibitors of phosphodieserase IV, J Computer-Aided Molecular Design, 15: 767785, 2001; US20120214791; WO2012168817; WO2013034755; WO2013034758; WO2013034761; WO2005041957; WO2005061497; WO2006024640; WO2013161913; WO2010136493; WO 2013098373; WO 2009016498; U.S. Pat. No. 6,573,263; M. Plummer et al., Bioorg Med Chem Lett 23(11), 3438, 2013; and M. Plummer et al., Bioorg Med Chem Lett 23(11), 3443, 2013.
An increase in vascular permeability has been shown to be attributable to an increase activity of PDE2. PDE2 and PDE3 in the endothelium can act as a sensor or switch to detect normal versus pathological concentrations of cGMP and thus regulate endothelial permeability accordingly with potential relevance to migraine. See Surapisitchat et al, Differential Regulation of Endothelial Cell Permeability by cGMP via Phosphodieserase 2 and 3, Circulation Research, 2007; 101, pgs.: 811-818 and Duran et al., The NO Cascade, eNOS Location and Microvascular Permeability, Cardiovascular Res. (2010) 87, 254-261. Cerebral vasodilation is considered a major cause of migraine. See P. C. Tfelt-Hansen and P. J. Koehler, One hundred years of migraine research: major clinical and scientific observations from 1910 to 2010, Headache, 2011. 51(5), 752-578 and D. K. Arulmozhi et al., Migraine: current therapeutic targets and future avenues, Current Vascular Pharmacology, 2006, 4(2), 117-128. Therefore, PDE2 inhibition may have utility as a treatment or prophylactic for migraine.
The need for new and improved PDE2 modulators believed to be useful for treating PDE2 conditions, diseases or disorders such as Alzheimer's disease, cognitive impairment associated with schizophrenia, depression, migraines, and the like continues to exist. Inhibitors of PDE2 are not only believed to be useful in treating schizophrenia but also a wide variety of conditions or disorders that would benefit from increasing levels of cAMP and/or cGMP within neurons, including a variety neurological, psychotic, anxiety and/or movement disorders. Accordingly, agents that inhibit PDE2 and PDE2A would be desirable as therapeutics for neurological and psychiatric disorders.